The invention relates to a potentiometric, ion-selective electrode for measuring the cation concentration in a sample, which electrode is made of electrically conductive electrode material applied on an electrically insulating substrate using a thick-film technique and covered in the measurement area by an ion-sensitive membrane, preferably a liquid polymeric membrane.
The use of ion-sensitive electrodes (ISEs) for determination of the concentration or the activity of ions in aqueous media has been known for a long time. Conventional ISEs generally consist of an ion-sensitive membrane, which has at least one ion-sensitive component, and is placed in a plastic housing in such a way that one side of the membrane is contacted by the sample whose concentration or activity is to be determined, while the other side is in contact with an aqueous solution of precisely defined concentration, i.e. the so-called internal electrolyte. The presence of the internal electrolyte is characteristic for this type of electrode; its constant composition together with the integrated internal reference system (usually Ag/AgCl) will guarantee stable potentials and thus accurate and reliable measurements of concentration or activity. A detailed description of the structure and function of ion-sensitive electrodes can be found in “Chemical Sensors and Biosensors for Medical and Biological Applications”, Wiley-VCH, 1998, for example. On page 161 of this publication the structure and function of a liquid polymeric membrane is described. ISEs of this conventional type suffer from the disadvantage that, due to the aqueous component (i.e., the internal electrolyte), they are failure-prone, costly, difficult to manufacture, and that the possibilities for miniaturization are limited.